Skull o/Tisodus Ovveni, ^359 



The supraoccipital bone also appears as a navrow band at 

 the hinder margin of the cranial roof (fig. 1, s.occ.) bordering 

 the pair of verj short and broad parietal elements (pa.). 

 These bones are not symmetrical, the mesial suture being 

 bent and distorted to the right. They are much smaller tiian 

 the squamosals (sq.), of wiiich that of the left side is pre- 

 served to a large extent. The frontal bones (fr.) are rela- 

 tively enormous, and all the smaller roof-bones by which they 

 would be bounded laterally and anteriorly are unfortunately 

 removed. While for the most part flat, this pair of bones is 

 mesially depressed in the hinder two thirds of its extent, and 

 thus originates a great hollow gradually deepening forwards 

 to a sudden termination. 



Of the bones in the otic region only portions of the pro-otic 

 and opisthotic remain, and these are not sufficiently well 

 preserved for description. 



The three teeth displayed in their sockets in the para- 

 sphenoid bone (fig. 3, pas.) have been much worn during the 

 life of the fish, all the gano-dentine being removed from the 

 top of the flattened crown. 



Nothing further need be added to indicate how closely the 

 cranium thus described resembles that of Albula treated by 

 Dr. Shufeldt in the memoir already referred to. So far as 

 preserved the fossil agrees with the recent skull even to minute 

 particulars, and, apart from size, there is little to indicate 

 specific, much less generic, differences. The rostral region 

 may, however, have presented a different configuration from 

 that of the existing Albula ; and in the absence of all know- 

 ledge of the trunk it is impossible to arrive at any definite 

 generic determination. The Eocene fish from Sheppey must 

 therefore retain its provisional name of Pisodus Oweni^ and 

 the description of the skull now published merely establishes 

 its family position. 



EXPLANATION OF PLATE XVII. 



Pisodus Oiveni, Owen (ex Agassiz, MS.). Skull shown from four aspects, 

 one half the natural size. — London Clay, Isle of Sheppey. [Brit. 

 Mus. no. 39439.] 



Fig. 1. Cranial roof, c, base of crest on supraoccipital ; fr., frontal ; pa., 

 parietal; s.occ, supraoccipital; 55'., squamosal. 



Fiy. 2. Outline of occipital face, e.v.occ, exoccipital ; /. ?»., foramen 

 magnum. 



Fiy. 3. Base, pas., parasphenoid, showing- three teeth and sockets of 

 others. 



Fiy. 4. Side view, orb., position of eye. 



26* 



